[Bug]: Thread sidebar briefly empties after returning from Settings

Before submitting

• I searched existing issues and did not find a duplicate.
• I included enough detail to reproduce or investigate the problem.

Area

apps/web

Steps to reproduce

1. Start the web app from current main with at least one thread in the sidebar.
2. Open Settings from the lower-left sidebar action.
3. Select Back to return to the thread.

Expected behavior

The existing thread list should be present as soon as the thread sidebar returns.

Actual behavior

The thread-list region briefly renders empty, then the existing rows fade and scale back in. Settings replaces the thread sidebar in the React tree. While it is absent, the project projection remains subscribed but the thread-shell projection does not. Returning also remounts the animated list; the drag-and-drop accessibility nodes are installed just after mount, which makes FormKit treat the existing rows as additions and run its 225 ms add animation.

Impact

Cosmetic issue

Version or commit

main @ e72350122

Environment

macOS, T3 Code web development client, Node 24.13.1

Logs or stack traces

No console errors are emitted during the transition.

Workaround

Wait for the thread rows to reappear.

Related work

• #5930 retains the project projection across Settings, but not thread shells.
• #6480 preserves the project filter when navigating through Settings; it does not address projection retention.

Start in apps/web and reproduce the Settings-to-thread transition from main with an existing sidebar thread. Inspect the thread sidebar and Settings return path, including the projection subscription and animated list mount described in the issue. Done means existing rows remain present immediately on return without the transient empty state or add animation.